As for a substrate processing apparatus, there is known a plasma processing apparatus for processing a substrate by using a plasma. The plasma processing apparatus includes an evacuable processing chamber for generating a plasma therein and accommodating a wafer as a substrate to be processed. Provided in the chamber are various components (hereinafter, referred to as “structural members”) such as a mounting table (susceptor) for mounting thereon a wafer; a shower head (upper electrode plate) disposed above the susceptor so as to face the susceptor, for introducing a processing gas into the chamber; a focus ring (F/R) installed around an outer peripheral portion of the susceptor and surrounding the substrate to be processed; and the like.
Due to the presence of the focus ring, a plasma distribution region in the chamber extends from above the wafer to above the focus ring. Therefore, a plasma density at a peripheral portion of the wafer is maintained at a level substantially equal to that at a central portion of the wafer W. Accordingly, uniformity of plasma processing on the entire surface of the wafer is ensured.
In the chamber for performing plasma processing on the wafer, there is a need to prevent generation of particles causing contamination in order to increase a production yield of the wafer. For that reason, the structural members in the chamber are preferably made of dense materials. The dense materials can be obtained by a CVD (Chemical Vapor Deposition) method. Accordingly, for example, a focus ring is preferably manufactured by cutting a lump of material (bulk material) obtained by the CVD method.
Generally, the materials of the structural members include silicon (Si), silicon carbide (SiC) and the like. In case of Si, however, a dense bulk material cannot be obtained from Si by the CVD method. Hence, when manufacturing the focus ring from a dense bulk material, SiC to which the CVD method can be applied is preferably used as a material of the focus ring. Further, although SiC can be subjected to a sintering method, the sintering method is not suitable for forming the dense bulk material unlike the CVD method. If a structural member formed by cutting a bulk material obtained by the sintering method is provided in the chamber, it may be a cause of generation of particles.
Therefore, recently, SiC is preferably used as a material of a structural member such as a focus ring or the like (see, e.g., Japanese Patent Application Publication No. 2005-064460). The CVD method is used to form the structural member such as the focus ring or the like. A bulk material obtained by the CVD method is denser than that obtained by the sintering method, and thus is properly used as a material of a structural member which suppresses generation of particles.
Microcracks generated during the process of forming a bulk material of SiC obtained by the CVD method lead to formation of a fragmental layer having a thickness of about 20 μm on a surface of, e.g., the focus ring manufactured by cutting the bulk material. This fragmental layer causes generation of particles. In other words, when the focus ring having the fragmental layer is provided in the chamber of the plasma processing apparatus, particles are generated by the fragmental layer until the fragmental layer is removed, and this decreases a production yield of the wafer. A fragmental layer caused by microcracks is also found in a brittle member such as silicon (Si), quartz, alumina ceramic or the like.
Thus, various surface processing methods have been studied to remove a fragmental layer formed on a surface of a structural member such as a focus ring or the like of the plasma processing apparatus.
However, as the surface processing method, a wet process using a liquid chemical, e.g., hydrofluoric acid, nitric acid or the like, cannot be used because SiC is stable to various liquid chemicals. Also, mechanical polishing using an abrasive is suitable for a flat portion such as a backside or a side surface of the focus ring, but is not suitable for a corner of a stepped portion thereof. Therefore, it is common to remove the fragmental layer by a manual polishing operation, which requires a high cost and a long polishing time.